The present invention generally relates to the registration of semiconductor wafers undergoing work in process modules and, in particular, relates to a method for co-registering semiconductor wafers undergoing work in one or more blind process modules.
A process for measuring the thickness of an outer material layer of a semiconductor wafer is known as a wafer metrology process. During such a wafer metrology process, a semiconductor wafer is mechanically registered to a stage in a wafer metrology instrument. The wafer metrology instrument generates a map that indicates the thickness of an outer material layer of the semiconductor wafer over an entire surface of the wafer. This outer material layer thickness map is used by another instrument that thins, or etches, the outer material layer to a desired thickness. The outer layer thinning, or etching, instrument includes some type of tool that is directed onto the surface of the wafer. This tool must be properly positioned along the surface of the wafer to ensure that the thinning, or etching, process is performed at the correct location on the wafer surface. To ensure that the wafer is properly processed, an accurate correlation between the outer material layer thickness map and the position of the wafer with respect to the thinning, or etching, tool is required. This correlation between the outer material layer thickness map and the position of the wafer with respect to the thinning, or etching tool is accomplished by registering, or co-registering, the wafer to both the wafer metrology instrument and the thinning, or etching instrument in a consistent and repeatable manner.
The current approach for consistently co-registering a semiconductor wafer to both metrology and thinning, or etching instruments begins by marking, or scribing, the wafer with a set of alignment fiducials during the metrology process. The wafer is then placed in the etching instrument on a larger diameter wafer which serves as a surround. The surround is made of the same material as the wafer undergoing work to maintain a consistent reaction in the thinning, or etching, process along the edge of the wafer. The flat of the fiducialized wafer is then abutted to a flat of a registration surface, also made of the same material as the wafer for the same reason as the surround, that is taped to the surface of the surround, thereby registering the wafer in one direction. The wafer metrology fiducials are then visually aligned with a corresponding set of scribe marks on an aluminum holding plate, or platen, in the thinning, or etching instrument. Once aligned, two additional registration surfaces, also made of the same material as the wafer for the same reason as the surround, and the first registration surface, are abutted against the wafer and taped to the surround to maintain the position of the wafer. The surround is then taped to the platen and the thinning, or etching, process may begin.
As can be readily determined, the above-described co-registration procedure is time consuming and prone to human error. Furthermore, the above-described co-registration procedure includes scribing the water which produces particulate contamination that can adversely affect the thinning, or etching, process. Also, the use of scribe marks requires viewing into the thinning, or etching, instrument to perform the visual alignment. However, many instruments cannot be opened regularly and quickly to perform such a visual alignment, and many do not allow interior cameras to be used due to corrosive processes.
Accordingly, it would be desirable to provide a method for co-registering a semiconductor wafer undergoing work in one or more blind processing instruments without the need for scribing the wafer or visually aligning the wafer in an instrument.